Laser systems utilizing cellular-core optical fibers for beam shaping

ABSTRACT

In various embodiments, the beam parameter product and/or beam shape of a laser beam is adjusted by directing the laser beam across a path along the input end of a cellular-core optical fiber. The beam emitted at the output end of the cellular-core optical fiber may be utilized to process a workpiece.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/082,604, filed Oct. 28, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/522,893, filed Jul. 26, 2019, which is acontinuation of U.S. patent application Ser. No. 15/879,500, filed Jan.25, 2018, which claims the benefit of and priority to U.S. ProvisionalPatent Application No. 62/450,793, filed Jan. 26, 2017, the entiredisclosure of each of which is hereby incorporated herein by reference.

TECHNICAL FIELD

In various embodiments, the present invention relates to laser systems,specifically laser systems with controllable beam profiles, e.g.,variable beam shapes.

BACKGROUND

High-power laser systems are utilized for a host of differentapplications, such as welding, cutting, drilling, and materialsprocessing. Such laser systems typically include a laser emitter, thelaser light from which is coupled into an optical fiber (or simply a“fiber”), and an optical system that focuses the laser light from thefiber onto the workpiece to be processed. Wavelength beam combining(WBC) is a technique for scaling the output power and brightness fromlaser diodes, laser diode bars, stacks of diode bars, or other lasersarranged in a one- or two-dimensional array. WBC methods have beendeveloped to combine beams along one or both dimensions of an array ofemitters. Typical WBC systems include a plurality of emitters, such asone or more diode bars, that are combined using a dispersive element toform a multi-wavelength beam. Each emitter in the WBC systemindividually resonates, and is stabilized through wavelength-specificfeedback from a common partially reflecting output coupler that isfiltered by the dispersive element along a beam-combining dimension.Exemplary WBC systems are detailed in U.S. Pat. No. 6,192,062, filed onFeb. 4, 2000, U.S. Pat. No. 6,208,679, filed on Sep. 8, 1998, U.S. Pat.No. 8,670,180, filed on Aug. 25, 2011, and U.S. Pat. No. 8,559,107,filed on Mar. 7, 2011, the entire disclosure of each of which isincorporated by reference herein.

Optical systems for laser systems are typically engineered to producethe highest-quality laser beam, or, equivalently, the beam with thelowest beam parameter product (BPP). The BPP is the product of the laserbeam's divergence angle (half-angle) and the radius of the beam at itsnarrowest point (i.e., the beam waist, the minimum spot size). That is,BPP=NA×D/2, where D is the focusing spot (the waist) diameter and NA isthe numerical aperture; thus, the BPP may be varied by varying NA and/orD. The BPP quantifies the quality of the laser beam and how well it canbe focused to a small spot, and is typically expressed in units ofmillimeter-milliradians (mm-mrad). A Gaussian beam has the lowestpossible BPP, given by the wavelength of the laser light divided by pi.The ratio of the BPP of an actual beam to that of an ideal Gaussian beamat the same wavelength is denoted M², which is a wavelength-independentmeasure of beam quality.

In many laser-processing applications, the desired beam shape, spotsize, divergence, and beam quality may vary depending on, for example,the type of processing and/or the type of material being processed. Thisis particularly true for industrial lasers in material processingapplications. For example, a lower BPP value, i.e., a better beamquality, may be preferred for cutting a thin metal, while a larger BPP(i.e., a worse beam quality) may be preferred for cutting throughthicker metals. In order to change the BPP or beam shape in conventionallaser systems, frequently the output optical system must be swapped outwith other components and/or realigned, a time-consuming and expensiveprocess that may even lead to inadvertent damage of the fragile opticalcomponents of the laser system. Thus, there is a need for alternativetechniques for varying the BPP and/or beam shape of a laser system thatdo not involve such adjustments to the laser beam or optical system atthe output of the optical fiber.

SUMMARY

In accordance with embodiments of the present invention, laser systemsproduce beams that are directed into one or more core regions of acellular-core optical fiber in order to alter the beam shape and/or BPP.(Such beams are the “input beams” with reference to the optical fiberand may be simply “beams” or “output beams” with reference to the lasersystem initially generating the beam.) In various embodiments, theoptical fiber has an inter-core cladding that extends between and aroundthe various core regions; in various embodiments, all or a portion ofthe beam may be directed into this inter-core region in order to alterthe BPP of the ultimate output beam. The optical fiber may have one ormore outer cladding layers that confine the beam energy in the coreregions and/or the inter-core region.

The beam may be modulated such that it is only directed into variousones of the core regions without significant emission when the beam ismoved between the core regions. In other embodiments, the beam is movedfrom core region to core region without modulation—i.e., variations inpower level—therebetween (or with modulation to a different non-zero,finite power level, either higher or lower than the power level at whichthe beam is emitted into the core region(s)), and thus portions of thebeam power may be coupled into the inter-core cladding region. Invarious embodiments, the beam may be modulated at different power levelswhen it is directed into different ones of the core regions such thatdifferent amounts of beam power are coupled into different core regions.Instead or in addition, the beam may be directed toward different onesof the core regions for different times such that the time-averagedpower levels coupled into different core regions are different. The coreregions themselves may have different cross-sectional shapes and/orsizes that determine, at least in part, the final shape of the beamemitted from the optical fiber. In other embodiments, one or more (oreven all) of the core regions have substantially the same shape (e.g.,circular) and/or size, and the final shape of the beam is determined, atleast in part, by the translation of the beam among different ones ofthe core regions and/or the amount of beam power coupled into thedifferent core regions and/or the amount of beam power coupled into theinter-core cladding region. In various embodiments, at least a portionof the beam power may be coupled into one or more of the outer claddinglayers, at least for some amount of time, to alter the shape and/or BPPof the output beam.

As utilized herein, changing the “shape” of a laser beam refers toaltering the shape and geometric extent of the beam (e.g., at a point atwhich the beam intersects a surface). Changes in shape may beaccompanied by changes in beam size, angular intensity distribution ofthe beam, and BPP, but mere changes in beam BPP are not necessarilysufficient to change laser beam shape and vice versa.

Herein, “optical elements” may refer to any of lenses, mirrors, prisms,gratings, and the like, which redirect, reflect, bend, or in any othermanner optically manipulate electromagnetic radiation. Herein, beamemitters, emitters, or laser emitters, or lasers include anyelectromagnetic beam-generating device such as semiconductor elements,which generate an electromagnetic beam, but may or may not beself-resonating. These also include fiber lasers, disk lasers, non-solidstate lasers, etc. Generally, each emitter includes a back reflectivesurface, at least one optical gain medium, and a front reflectivesurface. The optical gain medium increases the gain of electromagneticradiation that is not limited to any particular portion of theelectromagnetic spectrum, but that may be visible, infrared, and/orultraviolet light. An emitter may include or consist essentially ofmultiple beam emitters such as a diode bar configured to emit multiplebeams. The input beams received in the embodiments herein may besingle-wavelength or multi-wavelength beams combined using varioustechniques known in the art. In addition, references to “lasers,” “laseremitters,” or “beam emitters” herein include not only single-diodelasers, but also diode bars, laser arrays, diode bar arrays, and singleor arrays of vertical cavity surface-emitting lasers (VCSELs).

Output beams produced in accordance with embodiments of the presentinvention may be utilized to process a workpiece such that the surfaceof the workpiece is physically altered and/or such that a feature isformed on or within the surface, in contrast with optical techniquesthat merely probe a surface with light (e.g., reflectivitymeasurements). Exemplary processes in accordance with embodiments of theinvention include cutting, welding, drilling, and soldering. Variousembodiments of the invention may also process workpieces at one or morespots or along a one-dimensional linear or curvilinear processing path,rather than flooding all or substantially all of the workpiece surfacewith radiation from the laser beam. Such one-dimensional paths may becomposed of multiple segments, each of which may be linear orcurvilinear.

One advantage of variable shape and/or BPP is improved laser applicationperformance for different types of processing techniques or differenttypes of materials being processed. Embodiments of the invention mayalso utilize various techniques for varying BPP and/or shape of laserbeams described in U.S. patent application Ser. No. 14/632,283, filed onFeb. 26, 2015, U.S. patent application Ser. No. 14/747,073, filed Jun.23, 2015, U.S. patent application Ser. No. 14/852,939, filed Sep. 14,2015, U.S. patent application Ser. No. 15/188,076, filed Jun. 21, 2016,U.S. patent application Ser. No. 15/479,745, filed Apr. 5, 2017, andU.S. patent application Ser. No. 15/649,841, filed Jul. 14, 2017, thedisclosure of each of which is incorporated in its entirety herein byreference.

Embodiments of the invention may be utilized with wavelength beamcombining (WBC) systems that include a plurality of emitters, such asone or more diode bars, that are combined using a dispersive element toform a multi-wavelength beam. Each emitter in the WBC systemindividually resonates, and is stabilized through wavelength-specificfeedback from a common partially reflecting output coupler that isfiltered by the dispersive element along a beam-combining dimension.Exemplary WBC systems are detailed in U.S. Pat. No. 6,192,062, filed onFeb. 4, 2000, U.S. Pat. No. 6,208,679, filed on Sep. 8, 1998, U.S. Pat.No. 8,670,180, filed on Aug. 25, 2011, and U.S. Pat. No. 8,559,107,filed on Mar. 7, 2011, the entire disclosure of each of which isincorporated by reference herein. Multi-wavelength output beams of WBCsystems may be utilized as input beams in conjunction with embodimentsof the present invention for, e.g., BPP and/or beam shape control.

In an aspect, embodiments of the invention feature a laser system thatincludes, consists essentially of, or consists of a beam emitter foremission of an input laser beam, a cellular-core optical fiber, areflector for receiving the input laser beam and reflecting the inputlaser beam toward the cellular-core optical fiber, an optical element,and a controller. The cellular-core optical fiber has an input end andan output end opposite the input end. The cellular-core optical fiberincludes, consists essentially of, or consists of a plurality of coreregions, and an inter-core cladding region surrounding and extendingbetween the core regions. The cellular-core optical fiber may include anouter cladding surrounding the inter-core cladding region. Therefractive index of at least one (or even each) of the core regions islarger than a refractive index of the inter-core cladding region. Theoptical element receives the input laser beam from the reflector andfocuses the input laser beam toward (e.g., to strike) the input end ofthe cellular-core optical fiber. The controller controls relative motionbetween the input end of the cellular-core optical fiber and thereflector and/or the optical element to thereby direct the input laserbeam along a path across the input end of the cellular-core opticalfiber. The path may include, consist essentially of, or consist of oneor more of the core regions. The path may include, consist essentiallyof, or consist of at least a portion of the inter-core cladding region.The path may include, consist essentially of, or consist of one or moreof the core regions and at least a portion of the inter-core claddingregion. A beam shape and/or a beam parameter product of an output beamemitted at the output end of the cellular-core optical fiber isdetermined at least in part by the path of the input laser beam.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The controller may be configured todirect the input laser beam along a path comprising a plurality of coreregions. The controller may be configured to modulate the output powerof the input laser beam as the input laser beam is directed along thepath. For example, the output power level of the input laser beam may bedifferent when the input laser beam is directed into different coreregions and/or into the inter-core cladding region. The controller maybe configured to reduce an output power of the input laser beam alongportions of the path over (i.e., intersecting) the inter-core claddingregion, thereby reducing or substantially eliminating coupling of beamenergy into the inter-core cladding region. The path may include,consist essentially of, or consist of all or a portion of the inter-corecladding region. Beam energy coupled into the inter-core cladding regionmay contribute a non-zero background energy level to the output beam.The output beam may include, consist essentially of, or consist of aplurality of discrete beams at the output end of the cellular-coreoptical fiber. The plurality of discrete beams may merge into fewerbeams (e.g., one beam) at a distance spaced away from the output end ofthe cellular-core optical fiber.

At least two of the core regions of the cellular-core optical fiber maydiffer in size and/or shape. The refractive index of the inter-corecladding region may be greater than or approximately equal to arefractive index of the outer cladding, if the outer cladding ispresent. The relative motion between the input end of the cellular-coreoptical fiber and the reflector and/or the optical element may include,consist essentially of, or consist of rotation of the reflector,rotation of the optical element, translation of the reflector,translation of the optical element, rotation of the input end of thecellular-core optical fiber, and/or translation of the input end of thecellular-core optical fiber. The optical element may include, consistessentially of, or consist of one or more lenses, one or more gratings(e.g., diffraction gratings), and/or one or more prisms. The system mayinclude one or more actuators for controlling motion of the reflector,the optical element, and/or the input end of the cellular-core opticalfiber. An input end cap may be disposed on the input end of thecellular-core optical fiber. An output end cap may be disposed on theoutput end of the cellular-core optical fiber.

The controller may be configured for feedback operation to progressivelyadjust the path along which the laser beam is directed on the input endof the cellular-core optical fiber based on a measured parameter. Themeasured parameter may be a measured parameter of a workpiece to beprocessed by the laser beam (e.g., composition, thickness, height ordepth of a surface feature, reflectivity, etc.) and/or of the laser beam(e.g., the laser beam proximate the output end of the cellular-coreoptical fiber). The measured parameter of the laser beam may be, forexample, flux density, beam shape, beam parameter product, beamdiameter, beam intensity, beam intensity as a function of areal beamlocation, etc. At least two of the core regions of the cellular-coreoptical fiber may have different cross-sectional shapes. Each of thecore regions of the cellular-core optical fiber may have the samecross-sectional shape (and two or more may have the same size ordifferent sizes). The plurality of core regions of the cellular-coreoptical fiber may include, consist essentially of, or consist of (i) acentral core region and (ii) a plurality of outer core regions disposedaround the central core region. The diameter (or other parameter such aswidth, side length, etc.) of the central core region may be greater thanthat of at least one (or even all) of the outer core regions. Thecontroller may be configured to increase the beam parameter product ofthe laser beam by directing the input laser beam along a path across theinput end of the cellular-core optical fiber that intersects theinter-core cladding region.

The controller may be configured to determine the beam shape and/or thebeam parameter product based at least in part on a characteristic of aworkpiece proximate the output end of the optical fiber into which thelaser beam is coupled. The characteristic of the workpiece may include,consist essentially of, or consist of a thickness of the workpiece, acomposition of the workpiece, a reflectivity of the workpiece, and/orthe height or depth of a surface feature on the workpiece. The systemmay include a memory, accessible to the controller, for storing datacorresponding to a processing path defined on the workpiece. Theprocessing path may include at least one directional change. Theprocessing path may be composed of one or more linear segments and/orone or more curvilinear segments. The controller may be configured toalter the output power, beam shape, and/or beam parameter product of thebeam along the processing path. The memory may be at least in partresident in the controller and/or at least in part resident remotely(e.g., network storage, cloud storage, etc.). The system may include adatabase for storing processing data for a plurality of materials. Thecontroller may be configured to query the database to obtain processingdata for one or more materials of the workpiece, and the beam shapeand/or the beam parameter product of the beam may be determined at leastin part by the obtained processing data.

The beam emitter may include, consist essentially of, or consist of oneor more beam sources emitting a plurality of discrete beams, focusingoptics for focusing the plurality of beams onto a dispersive element, adispersive element for receiving and dispersing the received focusedbeams, and a partially reflective output coupler positioned to receivethe dispersed beams, transmit a portion of the dispersed beamstherethrough as the input laser beam, and reflect a second portion ofthe dispersed beams back toward the dispersive element. The input laserbeam may be composed of multiple wavelengths. Each of the discrete beamsmay have a different wavelength. The second portion of the dispersedbeams may propagate back to the one or more beam sources to therebystabilize the beams to their emission wavelengths. The focusing opticsmay include or consist essentially of one or more cylindrical lenses,one or more spherical lenses, one or more spherical mirrors, and/or oneor more cylindrical mirrors. The dispersive element may include, consistessentially of, or consist of one or more diffraction gratings (e.g.,one or more transmissive gratings and/or one or more reflectivegratings), one or more dispersive fibers, and/or one or more prisms.

The controller may be configured to receive a desired beam parameter ofthe output beam and determine the path across the input end of thecellular-core optical fiber based at least in part thereon. The desiredbeam parameter may include, consist essentially of, or consist of thebeam parameter product and/or the beam shape of the output beam. Thecontroller may be configured to determine the path across the input endof the cellular-core optical fiber based at least in part on a sensed(e.g., measured) beam parameter proximate the output end of thecellular-core optical fiber (e.g., at the output end, within a laserhead attached to the output end, or on or near the surface of aworkpiece to be processed).

In another aspect, embodiments of the invention feature a method ofaltering a beam shape and/or a beam parameter product of a laser beam. Acellular-core optical fiber is provided. The cellular-core optical fiberhas an input end and an output end opposite the input end. Thecellular-core optical fiber includes, consists essentially of, orconsists of a plurality of core regions, and an inter-core claddingregion surrounding and extending between the core regions. Thecellular-core optical fiber may include an outer cladding surroundingthe inter-core cladding region. The refractive index of at least one (oreven each) of the core regions is larger than a refractive index of theinter-core cladding region. An input laser beam is directed across theinput end of the cellular-core optical fiber along a path thereon. Thepath may include, consist essentially of, or consist of one or more ofthe core regions. The path may include, consist essentially of, orconsist of at least a portion of the inter-core cladding region. Thepath may include, consist essentially of, or consist of one or more ofthe core regions and at least a portion of the inter-core claddingregion. A beam shape and/or a beam parameter product of an output beamemitted at the output end of the cellular-core optical fiber isdetermined at least in part by the path of the input laser beam.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The path may include, consistessentially of, or consist of a plurality of core regions. The outputpower of the input laser beam may be modulated as the input laser beamis directed along the path. For example, the output power level of theinput laser beam may be different when the input laser beam is directedinto different core regions and/or into the inter-core cladding region.The output power of the input laser beam may be reduced (e.g., to zeroor to near zero, or merely to a lower non-zero power) along portions ofthe path over (i.e., intersecting) the inter-core cladding region,thereby reducing or substantially eliminating coupling of beam energyinto the inter-core cladding region. The path may include, consistessentially of, or consist of all or a portion of the inter-corecladding region. Beam energy coupled into the inter-core cladding regionmay contribute a non-zero background energy level to the output beam.The output beam may include, consist essentially of, or consist of aplurality of discrete beams at the output end of the cellular-coreoptical fiber. The plurality of discrete beams may merge into fewerbeams (e.g., one beam) at a distance spaced away from the output end ofthe cellular-core optical fiber.

At least two of the core regions of the cellular-core optical fiber maydiffer in size and/or shape. The refractive index of the inter-corecladding region may be greater than or approximately equal to arefractive index of the outer cladding, if the outer cladding ispresent. An input end cap may be disposed on the input end of thecellular-core optical fiber. An output end cap may be disposed on theoutput end of the cellular-core optical fiber. A workpiece disposedproximate the output end of the cellular-core optical fiber may beprocessed with the output beam. The beam parameter product and/or thebeam shape of the output laser beam may be determined, via selection ofthe path across the input end of the cellular-core optical fiber, basedat least in part of a characteristic of the workpiece. Thecharacteristic of the workpiece may include, consist essentially of, orconsist of a thickness of the workpiece, a composition of the workpiece,a reflectivity of the workpiece, and/or the height or depth of a surfacefeature on the workpiece. The path across the input end of thecellular-core optical fiber may intersects the inter-core claddingregion of the cellular-core optical fiber. Directing the input laserbeam along the path may include, consist essentially of, or consist of(i) reflecting the laser beam with one or more reflectors and/or (ii)focusing the laser beam with one or more optical elements.

The input laser beam may be emitted from a beam emitter. The beamemitter may include, consist essentially of, or consist of one or morebeam sources emitting a plurality of discrete beams, focusing optics forfocusing the plurality of beams onto a dispersive element, a dispersiveelement for receiving and dispersing the received focused beams, and apartially reflective output coupler positioned to receive the dispersedbeams, transmit a portion of the dispersed beams therethrough as theinput laser beam, and reflect a second portion of the dispersed beamsback toward the dispersive element. The input laser beam may be composedof multiple wavelengths. Each of the discrete beams may have a differentwavelength. The second portion of the dispersed beams may propagate backto the one or more beam sources to thereby stabilize the beams to theiremission wavelengths. The focusing optics may include or consistessentially of one or more cylindrical lenses, one or more sphericallenses, one or more spherical mirrors, and/or one or more cylindricalmirrors. The dispersive element may include, consist essentially of, orconsist of one or more diffraction gratings (e.g., one or moretransmissive gratings and/or one or more reflective gratings), one ormore dispersive fibers, and/or one or more prisms.

A desired beam parameter of the output beam may be received, and thepath across the input end of the cellular-core optical fiber may beselected based at least in part on the desired beam parameter. Thedesired beam parameter may include, consist essentially of, or consistof the beam parameter product and/or the beam shape of the output beam.The path across the input end of the cellular-core optical fiber may beselected based at least in part on a sensed (e.g., measured) beamparameter proximate the output end of the cellular-core optical fiber(e.g., at the output end, within a laser head attached to the outputend, or on or near the surface of a workpiece to be processed).

In yet another aspect, embodiments of the invention feature a method ofprocessing a workpiece with a laser beam. A cellular-core optical fiberis provided. The cellular-core optical fiber has an input end and anoutput end opposite the input end. The cellular-core optical fiberincludes, consists essentially of, or consists of a plurality of coreregions, and an inter-core cladding region surrounding and extendingbetween the core regions. The cellular-core optical fiber may include anouter cladding surrounding the inter-core cladding region. Therefractive index of at least one (or even each) of the core regions islarger than a refractive index of the inter-core cladding region. Aworkpiece is disposed or positioned proximate (e.g., opticallydownstream of) the output end of the cellular-core optical fiber. A beamparameter product and/or a beam shape for processing of the workpiece isdetermined based on at least one characteristic of the workpiece. Alaser beam is directed toward (e.g., to strike) the input end of thecellular-core optical fiber. Thereafter and/or there during, the laserbeam is directed along a path across the input end of the cellular-coreoptical fiber to select the beam parameter product and/or the beam shapeof the laser beam emitted from the output end of the cellular-coreoptical fiber. The path may include, consist essentially of, or consistof one or more of the core regions. The path may include, consistessentially of, or consist of at least a portion of the inter-corecladding region. The path may include, consist essentially of, orconsist of one or more of the core regions and at least a portion of theinter-core cladding region. The workpiece is processed with the laserbeam emitted from the output end of the cellular-core optical fiber.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. Processing the workpiece may include,consist essentially of, or consist of physically altering at least aportion of and/or forming a feature on and/or in a surface of theworkpiece. Processing the workpiece may include, consist essentially of,or consist of cutting, welding, etching, annealing, drilling, soldering,and/or brazing. The at least one characteristic of the workpiece mayinclude, consist essentially of, or consist of a thickness of theworkpiece and/or a composition of the workpiece and/or a reflectivity ofthe workpiece. The path across the input end of the cellular-coreoptical fiber may intersect the inter-core cladding region of thecellular-core optical fiber, and beam energy coupled into thecellular-core cladding region may be utilized (at least in part) toprocess the workpiece. Directing the laser beam along the path acrossthe input end of the cellular-core optical fiber may include, consistessentially of, or consist of (i) reflecting the laser beam with one ormore reflectors and/or (ii) focusing the laser beam with one or moreoptical elements. The beam parameter product and/or the beam shape ofthe laser beam may be altered while and/or after processing theworkpiece by directing the laser beam onto a second path across theinput end of the cellular-core optical fiber, the second path beingdifferent from the path across the input end of the cellular-coreoptical fiber. The second path may include, consist essentially of, orconsist of one or more of the core regions. The second path may include,consist essentially of, or consist of at least a portion of theinter-core cladding region. The second path may include, consistessentially of, or consist of one or more of the core regions and atleast a portion of the inter-core cladding region. The second path mayinclude, consist essentially of, or consist of the same core region(s)and/or inter-core cladding region (or portion thereof) as the path, andthe time the beam spends intersecting one or more of the core regionsand/or the inter-core cladding region may be different in the secondpath. A second workpiece different from the first workpiece may beprocessed while the beam is being directed along the second path. Thesecond workpiece may have at least one characteristic (e.g., thickness,composition, reflectivity, etc.) different from that of the workpiece.

The input laser beam may be emitted from a beam emitter. The beamemitter may include, consist essentially of, or consist of one or morebeam sources emitting a plurality of discrete beams, focusing optics forfocusing the plurality of beams onto a dispersive element, a dispersiveelement for receiving and dispersing the received focused beams, and apartially reflective output coupler positioned to receive the dispersedbeams, transmit a portion of the dispersed beams therethrough as theinput laser beam, and reflect a second portion of the dispersed beamsback toward the dispersive element. The input laser beam may be composedof multiple wavelengths. Each of the discrete beams may have a differentwavelength. The second portion of the dispersed beams may propagate backto the one or more beam sources to thereby stabilize the beams to theiremission wavelengths. The focusing optics may include or consistessentially of one or more cylindrical lenses, one or more sphericallenses, one or more spherical mirrors, and/or one or more cylindricalmirrors. The dispersive element may include, consist essentially of, orconsist of one or more diffraction gratings (e.g., one or moretransmissive gratings and/or one or more reflective gratings), one ormore dispersive fibers, and/or one or more prisms.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations. As used herein, the term“substantially” means±10%, and in some embodiments, ±5%. The term“consists essentially of” means excluding other materials thatcontribute to function, unless otherwise defined herein. Nonetheless,such other materials may be present, collectively or individually, intrace amounts. Herein, the terms “radiation” and “light” are utilizedinterchangeably unless otherwise indicated. Herein, “downstream” or“optically downstream,” is utilized to indicate the relative placementof a second element that a light beam strikes after encountering a firstelement, the first element being “upstream,” or “optically upstream” ofthe second element. Herein, “optical distance” between two components isthe distance between two components that is actually traveled by lightbeams; the optical distance may be, but is not necessarily, equal to thephysical distance between two components due to, e.g., reflections frommirrors or other changes in propagation direction experienced by thelight traveling from one of the components to the other.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIGS. 1A and 1B are cross-sectional schematics of example cellular-coreoptical fibers in accordance with various embodiments of the invention;

FIG. 2 is a cross-sectional schematic of an example cellular-coreoptical fiber in accordance with various embodiments of the invention;

FIG. 3 is a schematic diagram of a laser system utilizing acellular-core optical fiber in accordance with various embodiments ofthe invention;

FIG. 4A is a cross-sectional schematic of an example cellular-coreoptical fiber in accordance with various embodiments of the invention;

FIG. 4B depicts two different input beam paths traversable along theface of the optical fiber of FIG. 4A in accordance with variousembodiments of the invention;

FIG. 5 depicts a series of time-averaged beam shapes of the input andoutput laser beams for an input beam traveling along one of the pathsdepicted in FIG. 4B in accordance with various embodiments of theinvention;

FIG. 6 depicts a series of time-averaged beam shapes of the input andoutput laser beams for an input beam traveling along one of the pathsdepicted in FIG. 4B in accordance with various embodiments of theinvention;

FIG. 7 is a cross-sectional schematic of an example cellular-coreoptical fiber in accordance with various embodiments of the invention;

FIGS. 8A and 8B depict two different input beam paths traversable alongthe face of the optical fiber of FIG. 7 in accordance with variousembodiments of the invention;

FIG. 9 depicts a series of time-averaged beam shapes of the input andoutput laser beams for an input beam traveling along the path depictedin FIG. 8A in accordance with various embodiments of the invention;

FIG. 10 depicts a series of time-averaged beam shapes of the input andoutput laser beams for an input beam traveling along the path depictedin FIG. 8B in accordance with various embodiments of the invention; and

FIG. 11 is a schematic diagram of a wavelength beam combining lasersystem that may be utilized to supply the input beam for laser beamdelivery systems in accordance with various embodiments of theinvention.

DETAILED DESCRIPTION

FIGS. 1A and 1B depict two different exemplary cellular-core fibers 100,110 usable in accordance with embodiments of the present invention. Asshown, each cellular-core fiber has multiple different core regions 120each having a refractive index (e.g., a refractive index n₀). (While allof the core regions 120 are described in this example as having the samerefractive index, embodiments of the invention include implementationsin which one or more of the core regions 120 have refractive indicesdifferent from the other core regions; such indices of refraction are,in generally, greater than the refractive index of the inter-corecladding region and/or the outer cladding.) While cellular-core fibers100, 110 are depicted as having variously shaped and numbers of coreregions 120 (e.g., substantially circular in cross-section for fiber 100and of different shapes (e.g., square, rectangular, triangular,elliptical, circular, etc.) for fiber 110), these are merely exemplary,and cellular-core fibers in accordance with embodiments of the inventionmay have two or more core regions 120, and the core regions 120 may havethe same size and/or shape or different sizes and/or shapes. As utilizedherein, a “cellular-core fiber” or “cellular-core optical fiber” has twoor more distinct core regions separated from each other and at leastpartially surrounded by an inter-core cladding region having arefractive index lower than that of at least one of the cores. Invarious embodiments, the core regions of a cellular-core fiber are notcoaxial; while one or more of the core regions may be annular, typicallya core region does not surround one of the other core regions in thecellular-core fiber.

An inter-core cladding region 130 is disposed between the various coreregions 120, and the inter-core cladding region 130 typically has anindex of refraction (e.g., an index of refraction n₁) that is less thanthat of at least one (and, in various embodiments, all) of the coreregions 120. The cellular-core fiber 100, 110 may also have an outercladding region 140 that surrounds the core regions 120 and theinter-core cladding 130, and the outer cladding region 140 may have anindex of refraction (e.g., an index of refraction n₂) that is less thanor approximately equal to the index of refraction of the inter-corecladding region 130. In various embodiments, one or more additionalouter cladding regions are disposed partially or completely around theouter cladding region 140, and each of the outer cladding regions mayhave the same or different refractive indices.

In various embodiments of the invention, the shape of an input beam isaltered by rapidly steering the beam between different ones of the coreregions 120 of a cellular-core fiber (e.g., fiber 100, fiber 110, oranother cellular-core fiber). Movement of the input beam in differentpatterns (i.e., among different ones of the core regions 120) generatesoutput beams from the optical fiber having different beam shapes. Invarious embodiments of the invention, the shape of the input beam may bealtered by directing the beam into differently shaped core regions ofthe cellular-core fiber 110. The shape of the core region(s) into whichthe input beam is directed helps to determine the shape of the outputbeam emitted from the optical fiber. In various embodiments, beam energydirected into the inter-core cladding region 130 (e.g., when the beam ismoved between different core regions 120) is at least partially confinedin the inter-core cladding region 130, particularly in embodiments inwhich the index of refraction n₂ of the outer cladding region 140 isless than the index of refraction n₁ of the inter-core cladding region130. Such beam power coupled into the inter-core cladding region 130typically results in a non-zero background power level at the output.This background power level may vary the BPP of the final output beam,which may be desirable in various different applications of the outputbeam (e.g., materials processes such as cutting or welding).

FIG. 2 depicts another exemplary cellular-core fiber 200 in accordancewith various embodiments of the present invention. The cellular-corefiber 200 is a fiber bundle in which multiple discrete optical fibers210, each having at least one core region 220 surrounded by a claddingregion 230, are bundled together via an “inter-core” or inter-fibermaterial 240 that may include, consist essentially of, or consist of amaterial that is at least partially transparent to light (e.g., lighttransmitted through the fibers 210). For example, the inter-fibermaterial 240 may include, consist essentially of, or consist of epoxy,glass, plastic, etc. As shown in FIG. 2 , the fiber bundle 200 may be atleast partially surrounded (e.g., at its outer periphery) by a ferrule250, which may include, consist essentially of, or consist of, e.g.,glass and/or metal. In various embodiments, the various individualfibers 210 of the fiber bundle 200 have different sizes and/or shapesand/or numbers of core regions 220. In various embodiments, emission ofthe input beam into the inter-fiber material 240 is avoided, as suchbeam power is typically lost (i.e., not emitted as part of the outputbeam from the fiber bundle 200) and may even damage the fiber bundle 200itself. Exemplary fiber bundles and systems utilizing them are alsodescribed in U.S. patent application Ser. No. 15/807,795, filed on Nov.9, 2017, the entire disclosure of which is incorporated by referenceherein.

In various embodiments, one or more of the fibers 200 may be step-cladoptical fibers as detailed in U.S. patent application Ser. No.15/479,745, filed on Apr. 5, 2017 (“the '745 application”), the entiredisclosure of which is incorporated by reference herein. As described inthe '745 application, a step-clad optical fiber may include, consistessentially of, or consist of a center core, a first claddingsurrounding the center core, an annular core surrounding the firstcladding, and a second cladding surrounding the annular core. Variousproperties of the first cladding may enable BPP variation based at leastin part on the power coupled into the first cladding. Other BPP and/orbeam shape variations may be achieved based on power coupled into otherportions of the step-clad optical fiber, either in addition to orinstead of the first cladding. As described in the '745 application, therefractive index (N₂) of the first cladding of a step-clad fiber has avalue between a high index N₁ (e.g., of the center core and/or of theannular core) and a low index N₃ (e.g., of the second cladding), so thatthe center core will have a smaller numerical aperture (NA), given bysqrt(N₁ ²−N₂ ²), than the NA of the annular core, given by sqrt(N₁ ²−N₃²). While in various embodiments the center core and an annular core ofa step-clad optical fiber are approximately equal to each other, invarious embodiments the index of refraction of the annular core may bedifferent from (i.e., either less than or greater than) the index ofrefraction of the center core; however, in general, the index ofrefraction of the annular core remains larger than the index ofrefraction of the first cladding. In various embodiments, as disclosedin the '745 application, the annular core may have the same refractiveindex as the first cladding, i.e., the annular core merges into thefirst cladding. Step-clad fibers in accordance with embodiments of theinvention may have substantially all or all of the laser power coupledinto the first cladding. More power coupled into the first cladding willgenerally lead to larger BPP. In various embodiments, the diameter ratioof the first cladding and the center core is larger than 1.2, e.g.,between 1.2 and 3, or even between 1.3 and 2.

In accordance with various embodiments of the invention, the variouscore, inter-core cladding, and outer cladding layers of optical fibersmay include, consist essentially of, or consist of glass, such assubstantially pure fused silica and/or fused silica doped with fluorine,titanium, germanium, and/or boron. Selection of proper materials toachieve the desired refractive indices in different portions of theoptical fibers may be performed by those of skill in the art withoutundue experimentation.

FIG. 3 depicts an exemplary laser system 300 utilizing cellular-corefiber in accordance with embodiments of the invention. As shown, thelaser system 300 includes a cellular-core fiber 305. A laser beam 310 isredirected by a reflector 315 (e.g., one or more mirrors) and coupledinto the fiber 305 via an optical element 320. Optical element 320 mayinclude, consist essentially of, or consist of, for example, one or morelenses (e.g., cylindrical and/or spherical lenses). As shown, one orboth ends of the fiber 305 may be terminated via an end cap 325 (e.g., aglass block). One or more surfaces of one or both end caps 325, and/orof the fiber 305 (e.g., in embodiments in which one or both end caps 325are not present) may be coated with an antireflection coating. The endcaps 325 may have lengths of, e.g., at least 5 mm. The lengths of theend caps 325 may be, e.g., 50 mm or less.

The cellular-core fiber 305 alters the shape and/or BPP of the beam 310,as detailed herein, and outputs an output beam 330 into, for example, alaser head 335. The laser head 335 may include, consist essentially of,or consist of, for example, additional focusing optics and/orpositioners utilized when output beam 330 is utilized for any of a hostof different applications (e.g., cutting, welding, etc.). The laser beam310 may be a multi-wavelength beam and may be generated by a WBC system,as described below; thus, in various embodiments the output beam 330 isalso a multi-wavelength beam. Laser head 335 may direct the output beamto a workpiece for processing thereof. In other embodiments, the laserhead 335 is omitted and the output beam is directed toward a workpiecedirectly from the fiber 305.

In various embodiments, movement of the reflector 315 translates thebeam 310 such that it is directed into one or more of the core regions(and/or into the inter-core cladding) of the cellular-core fiber 305.For example, the reflector 315 may be tip-tilt adjusted (e.g., rotated)along a path 340 in response to one or more actuators 345. In additionor alternatively, the reflector 315 may be translated within the beampath to direct the beam 310 into different regions of the fiber 305. Invarious embodiments, the system may utilize a deformable reflector 315to direct the beam, as detailed in U.S. patent application Ser. No.14/632,283, filed on Feb. 26, 2015, the entire disclosure of which isincorporated by reference herein.

The beam 310 may be translated to different ones of the core regions(and/or to the inter-core cladding) at a beam translation speed of,e.g., greater than approximately 10 mm/s, or even greater thanapproximately 100 mm/s. The beam translation speed may depend on, forexample, the operational speed of the actuator 345 and/or the focallength(s) of the optical element 320. As mentioned previously, duringtranslation of the beam 310, the output power of the beam may bemodulated. For example, the output power may be reduced, or evendecreased to near or approximately zero power, when the beam traversesthe inter-core cladding region in order to minimize in-coupling into theinter-core cladding region. In other embodiments, the output power ismaintained at approximately the same level when the beam is translatedfrom one or more core regions into the inter-core cladding, in order toin-couple more beam power into the inter-core cladding. The output powerof beam 310 may also be changed (i.e., increased or decreased) when thebeam is directed into different ones of the core regions of the fiber305. In addition or instead, the amount of time the beam is directedinto any particular region of the cellular-core fiber 305 (e.g., one ormore of the core regions and/or the inter-core cladding region) may bevaried so that the time-averaged power level coupled into such regionsis different.

In various embodiments, the actuator 345 is a dual-axis actuator that iscapable of tilting and/or moving the reflector 315 along two differentaxes (e.g., perpendicular x and y axes). In an embodiment, the mirror isturned at angles of θx and θy, which translates the focal spot of thebeam 310 on the input surface of the fiber 305 by an amount θx×f in thex-direction and θy×f in the y-direction, where the x- and y-directionsare perpendicular to the direction of beam propagation and f is thefocal length of the optical element 320. In other embodiments of theinvention, multiple different actuators and/or multiple differentreflectors may be utilized to translate the beam 310, and each actuatorand/or reflector may control translation along a single axis ordirection. In various embodiments, the optical element 320 may betranslated in addition to or instead of the reflector 315 being moved inorder to translate the beam 310 across the input surface of the fiber305. In various embodiments, the input surface of the fiber 305 (e.g.,the input end cap 325) may itself be translated in addition to orinstead of the reflector 315 and/or the optical element 320 being movedin order to translate the beam 310 across the input surface of the fiber305.

Laser systems in accordance with embodiments of the invention mayincorporate a controller 350 that controls the movement of the laserbeam 310 among the various core regions and/or the inter-core claddingof the cellular-core fiber 305. For example, the controller may controlthe movement (e.g., rotation and/or lateral movement) of reflector 315and/or optical element 320 (e.g., via one or more actuators 345) inorder to direct the laser beam 310 into different ones of the coreregions and/or into the inter-core cladding. The controller 350 may alsomove the input end of the fiber 104, in addition to or instead ofcontrolling reflector 315 and/or optical element 320, in order to couplethe laser beam 310 into different core regions and/or into theinter-core cladding. The controller 350 may also modulate the outputpower of the beam 310 as a function of the position of the beam relativeto the fiber 305 in order to, for example, control the amount of beampower coupled into various regions of the fiber 305. The controller 350may also alter the speed of the relative motion between thecellular-core fiber 305 and the reflector 315 and/or optical element 320in order to vary the amount of power coupled into various regions of thefiber 305 as a function of time.

The controller 350 may be provided as either software, hardware, or somecombination thereof. For example, the system may be implemented on oneor more conventional server-class computers, such as a PC having a CPUboard containing one or more processors such as the Pentium or Celeronfamily of processors manufactured by Intel Corporation of Santa Clara,Calif., the 680×0 and POWER PC family of processors manufactured byMotorola Corporation of Schaumburg, Ill., and/or the ATHLON line ofprocessors manufactured by Advanced Micro Devices, Inc., of Sunnyvale,Calif. The processor may also include a main memory unit for storingprograms and/or data relating to the methods described above. The memorymay include random access memory (RAM), read only memory (ROM), and/orFLASH memory residing on commonly available hardware such as one or moreapplication specific integrated circuits (ASIC), field programmable gatearrays (FPGA), electrically erasable programmable read-only memories(EEPROM), programmable read-only memories (PROM), programmable logicdevices (PLD), or read-only memory devices (ROM). In some embodiments,the programs may be provided using external RAM and/or ROM such asoptical disks, magnetic disks, as well as other commonly used storagedevices. For embodiments in which the functions are provided as one ormore software programs, the programs may be written in any of a numberof high level languages such as FORTRAN, PASCAL, JAVA, C, C++, C #,BASIC, various scripting languages, and/or HTML. Additionally, thesoftware may be implemented in an assembly language directed to themicroprocessor resident on a target computer; for example, the softwaremay be implemented in Intel 80×86 assembly language if it is configuredto run on an IBM PC or PC clone. The software may be embodied on anarticle of manufacture including, but not limited to, a floppy disk, ajump drive, a hard disk, an optical disk, a magnetic tape, a PROM, anEPROM, EEPROM, field-programmable gate array, or CD-ROM.

The controller 350 may compute a proper position of the input laser beamrelative to the fiber end face based on a desired value of a beamproperty (e.g., flux density, beam diameter, beam shape, BPP, etc.) at aworkpiece or at the laser head 335 and a known relationship between thebeam property and the position of the beam relative to the fiber endface (e.g., one or more of the core regions and/or the inter-corecladding); and/or based on user input (e.g., a commanded degree ofoverlap with or position on the fiber's end face or a portion thereof(e.g., one or more cores or inter-core cladding)); and/or, as explainedin greater detail below, may use feedback so that the optimal alignmentbetween the beam and the end face of the fiber is progressivelyattained. For example, a photodetector or other light sensor may beutilized proximate the workpiece to monitor the beam shape, beamdiameter, BPP, and/or flux density at the workpiece surface (forexample, the beam property of the beam itself, or via measurement of areflection from the workpiece surface), and the controller 350 mayutilize the measured value(s) as feedback to adjust the positioning ofthe input beam relative to the fiber end until the desired beam propertyis achieved at the workpiece. For example, the measured beam propertymay be iteratively compared to a desired beam property (e.g., one inputor otherwise determined by a user, and/or one determined by one or moreproperties of the workpiece and/or the type of processing for which thelaser is to be utilized), and the controller 350 may reduce or minimizethe difference therebetween via, e.g., minimization of an errorfunction. Other sensors may be utilized in addition or instead of lightsensors in embodiments of the invention, e.g., thermal sensors and/orsensors measuring the effect of the beam on the workpiece surface (e.g.,depth or profile sensors, etc.).

In various embodiments, the controller 350 may detect the beam shapeand/or BPP (or other beam property) resulting from various pathstraversed on the faces of various cellular-core optical fibers, storethe results, and utilize the results to determine one or more suitablepaths in response to a desired beam property such as beam shape or BPP.The results may even be utilized in a machine-learning model that may beutilized to predict one or more beam properties resulting from possiblepaths traversed by a laser beam on a given cellular-core optical fiber.In various embodiments, physical/optical modeling may be utilized topredict one or more beam properties (e.g., beam shape and/or BPP)resulting from various paths traversed on a variety of differentcellular-core fibers, and such results may be utilized, at least inpart, by controller 350 to select a path to achieve a desired beamproperty.

FIG. 4A is a schematic cross-section of an exemplary cellular-core fiber400 in accordance with embodiments of the present invention. As shown,this example fiber 400 has seven different core regions 120 spaced apartat substantially equal distances from each other, corresponding to acore spacing 410. The core regions 120 are surrounded by an inter-corecladding 130, which is in turn enclosed by an outer cladding layer orferrule 140. In the examples provided below, each core 120 has adiameter of 100 μm, the inter-core spacing 410 is 150 μm, the inter-corecladding 130 has a diameter of 500 μm and a numerical aperture of 0.12,and the outer cladding 140 has an outer diameter of 600 μm and anumerical aperture of 0.22. FIG. 4B depicts two different exemplary beampaths utilized to demonstrate embodiments of the present invention. Thefirst is an “arrow” path 420 proceeding among the center core region 120and the two core regions 120 adjacent to and slightly below the centercore region 120. The second path is a “ring” path 430 proceeding amongthe outer six core regions 120.

FIG. 5 depicts a series of simulated time-averaged beam shapes of theinput and output laser beams for the exemplary embodiment in which theinput beam is moved along the arrow path 420 depicted in FIG. 4B. In thesimulated images, the laser is a 4 kW WBC laser having a BPP ofapproximately 4 mm-mrad if coupled into a conventional 100 μm opticalfiber. The leftmost image depicts the input beam moving along the arrowpath 420, and the remaining images depict the resulting output beam atthe exit surface of the fiber 400 and at increasing distances away fromthe fiber exit. As shown, the laser power remains substantially constantover time as the laser beam is moved from one core region 120 toanother; thus, some of the laser power is coupled into the inter-corecladding region 130. This power coupled into the inter-core claddingregion 130 is evident in the remaining images as a non-zero backgroundoutput power level. As shown in FIG. 5 , the output beam emerges fromthe fiber 400 as three discrete beams that merge into a single shapedbeam beyond the fiber exit. In this manner, both the shape and the BPPof the input beam have been altered via control of the beam along path420 to form the desired output beam, which may be utilized to, e.g.,process a workpiece. For example, in FIG. 5 the estimated effective spotsize of the beam at the fiber exit is approximately 450 μm in diameter,and the BPP of the beam at the fiber exit is approximately 18 mm-mrad.

FIG. 6 depicts a series of simulated time-averaged beam shapes of theinput and output laser beams for the exemplary embodiment in which theinput beam is moved along the ring path 430 depicted in FIG. 4B. In thesimulated images, the laser is a 4 kW WBC laser having a BPP ofapproximately 4 mm-mrad if coupled into a conventional 100 μm opticalfiber. The leftmost image depicts the input beam moving along the ringpath 430, and the remaining images depict the resulting output beam atthe exit surface of the fiber 400 and at increasing distances away fromthe fiber exit. As shown, the laser power is modulated at the input inorder to prevent appreciable power being coupled into the inter-corecladding region 130. That is, the output power of the laser is decreasedto zero as the laser beam crosses over the inter-core cladding region130 when travelling from one core region 120 to another. As shown inFIG. 6 , the output beam emerges from the fiber 400 as six discretebeams that merge into a single shaped beam beyond the fiber exit. Inthis manner, both the shape and the BPP of the input beam have beenaltered via control of the beam along path 430 to form the desiredoutput beam, which may be utilized to, e.g., process a workpiece. Forexample, in FIG. 6 the estimated effective spot size of the beam at thefiber exit is approximately 365 μm in diameter, and the BPP of the beamat the fiber exit is approximately 14 mm-mrad.

FIG. 7 is a schematic cross-section of an exemplary cellular-core fiber700 in accordance with embodiments of the present invention. As shown,the fiber 700 has eight different outer core regions 710 that surroundan inner (or center) core region 720 having a larger diameter. The coreregions 710, 720 are surrounded by an inter-core cladding 130, which isin turn enclosed by an outer cladding layer 140. The center point of theinner core region 720 is separated from the center points of each of theouter core regions 710 by a spacing 730. In the examples provided below,each outer core 710 has a diameter of 100 μm, the inner core 720 has adiameter of 500 μm, the spacing 730 from the center of the inner core toany of the outer cores is 350 μm, and the inter-core cladding 130 has anouter diameter of 900 μm. FIGS. 8A and 8B depict two different exemplarybeam paths utilized to demonstrate embodiments of the present invention.The first path 800, shown in FIG. 8A, is a path proceeding among thecenter core region 720 and two of the outer core regions 710. As shownby the dashed line, the laser power is minimized or substantially offwhen the beam crosses over the inter-core cladding region 130. Thesecond path 810, shown in FIG. 8B, is similar to the path 800 of FIG. 8Aexcept that the laser power is also reduced or minimized when the laserbeam is at or near the center of the center core 720.

FIG. 9 depicts a series of simulated time-averaged beam shapes of theinput and output laser beams for the exemplary embodiment in which theinput beam is moved along the path 800 depicted in FIG. 8A. In thesimulated images, the laser is a 4 kW WBC laser having a BPP ofapproximately 4 mm-mrad if coupled into a conventional 100 μm opticalfiber. The leftmost image depicts the input beam moving along the path800, and the remaining images depict the resulting output beam at theexit surface of the fiber 700 and at increasing distances away from thefiber exit. As shown, the laser power is decreased, at least on atime-averaged basis, when the input beam is coupled into the two outercore regions 710 relative to the power level coupled into the centercore region 720 (i.e., the output power of the beam and/or the amount oftime spent over the outer core regions 710 may be less than when thebeam is directed into the center core region 720). When the output beamemerges from the fiber exit, it exits as a large primary beamaccompanied by two small “pilot beams.” Such pilot beams may beadvantageous in applications such as welding for pre-heating areas to beprocessed and/or for guiding the primary beam. As shown, the primarybeam has high output power at its center, and the output power decreasestoward the edges of the primary beam. In FIG. 9 the estimated effectivespot size of the beam at the fiber exit is approximately 490 μm indiameter, and the BPP of the beam at the fiber exit is approximately 20mm-mrad.

FIG. 10 depicts a series of simulated time-averaged beam shapes of theinput and output laser beams for the exemplary embodiment in which theinput beam is moved along the path 810 depicted in FIG. 8B. In thesimulated images, the laser is a 4 kW WBC laser having a BPP ofapproximately 4 mm-mrad if coupled into a conventional 100 μm opticalfiber. The leftmost image depicts the input beam moving along the path810, and the remaining images depict the resulting output beam at theexit surface of the fiber 700 and at increasing distances away from thefiber exit. As shown, the laser power is decreased, at least on atime-averaged basis, when the input beam is coupled into the two outercore regions 710. When the output beam emerges from the fiber exit, itexits as a large primary beam accompanied by two small pilot beams. Asshown, the output power of the primary beam is substantially uniform atand immediately beyond the fiber exit, i.e., the primary beam has aflat-top beam shape which may be advantageous for many applications suchas welding, cladding, etc. In FIG. 10 the estimated effective spot sizeof the beam at the fiber exit is approximately 495 μm in diameter, andthe BPP of the beam at the fiber exit is approximately 20 mm-mrad.

The controller 350 may, in accordance with the embodiments of theinvention, control the BPP and/or beam shape of the output beam based onthe type of desired processing (e.g., cutting, welding, etc.) and/or onone or more characteristics (e.g., materials parameters, thickness,material type, etc.) of the workpiece to be processed and/or of adesired processing path mapped out for the output beam. Such processand/or material parameters may be selected by a user from a storeddatabase in a memory associated with controller 350 or may be enteredvia an input device (e.g., touchscreen, keyboard, pointing device suchas a computer mouse, etc.). One or more processing paths may be providedby a user and stored in an onboard or remote memory associated withcontroller 350. After workpiece and/or processing path selection, thecontroller 350 queries the database to obtain the correspondingparameter values. The stored values may include a BPP and/or beam shapesuitable to the material and/or to one or more processing paths orprocessing locations on the material.

As is well understood in the plotting and scanning art, the requisiterelative motion between the beam and the desired beam path may beproduced by, for example, optical deflection of the beam using a movablemirror, physical movement of the laser using a gantry, lead-screw orother arrangement, and/or a mechanical arrangement for moving theworkpiece rather than (or in addition to) the beam. The controller 350may, in some embodiments, receive feedback regarding the position and/orprocessing efficacy of the beam relative to the workpiece from afeedback unit connected to suitable monitoring sensors. In response tosignals from the feedback unit, the controller 350 may alter the path,BPP and/or shape of the beam via, e.g., movement of the input beam 310to one or more different locations on the face of the cellular-coreoptical fiber. Embodiments of the invention may also incorporate aspectsof the apparatus and techniques disclosed in U.S. patent applicationSer. No. 14/639,401, filed on Mar. 5, 2015, U.S. patent application Ser.No. 15/261,096, filed on Sep. 9, 2016, and U.S. patent application Ser.No. 15/649,841, filed on Jul. 14, 2017, the entire disclosure of each ofwhich is incorporated by reference herein.

In addition, the laser system may incorporate one or more systems fordetecting the thickness of the workpiece and/or heights of featuresthereon. For example, the laser system may incorporate systems (orcomponents thereof) for interferometric depth measurement of theworkpiece, as detailed in U.S. patent application Ser. No. 14/676,070,filed on Apr. 1, 2015, the entire disclosure of which is incorporated byreference herein. Such depth or thickness information may be utilized bythe controller to control the output beam BPP and/or shape to optimizethe processing (e.g., cutting or welding) of the workpiece, e.g., inaccordance with records in the database corresponding to the type ofmaterial being processed.

Laser systems and laser delivery systems in accordance with embodimentsof the present invention and detailed herein may be utilized in and/orwith WBC laser systems. Specifically, in various embodiments of theinvention, multi-wavelength output beams of WBC laser systems may beutilized as the input beams for laser beam delivery systems forvariation of BPP and/or beam shape as detailed herein. FIG. 11 depictsan exemplary WBC laser system 1100 that utilizes one or more lasers1105. In the example of FIG. 11 , laser 1105 features a diode bar havingfour beam emitters emitting beams 1110 (see magnified input view 1115),but embodiments of the invention may utilize diode bars emitting anynumber of individual beams or two-dimensional arrays or stacks of diodesor diode bars. In view 1115, each beam 1110 is indicated by a line,where the length or longer dimension of the line represents the slowdiverging dimension of the beam, and the height or shorter dimensionrepresents the fast diverging dimension. A collimation optic 1120 may beused to collimate each beam 1110 along the fast dimension. Transformoptic(s) 1125, which may include, consist essentially of, or consist ofone or more cylindrical or spherical lenses and/or mirrors, are used tocombine each beam 1110 along a WBC direction 1130. The transform optics1125 then overlap the combined beam onto a dispersive element 1135(which may include, consist essentially of, or consist of, e.g., areflective or transmissive diffraction grating, a dispersive prism, agrism (prism/grating), a transmission grating, or an Echelle grating),and the combined beam is then transmitted as single output profile ontoan output coupler 1140. The output coupler 1140 then transmits thecombined beams 1145 as shown on the output front view 1150. The outputcoupler 1140 is typically partially reflective and acts as a commonfront facet for all the laser elements in this external cavity system1100. An external cavity is a lasing system where the secondary mirroris displaced at a distance away from the emission aperture or facet ofeach laser emitter. In some embodiments, additional optics are placedbetween the emission aperture or facet and the output coupler orpartially reflective surface. The output beam 1145 is a thus amultiple-wavelength beam (combining the wavelengths of the individualbeams 1110), and may be utilized as the input beam in laser beamdelivery systems detailed herein and/or may be coupled into an opticalfiber.

The terms and expressions employed herein are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:
 1. A method of forming a laser beam, the methodcomprising: providing a cellular-core optical fiber having an input endand an output end opposite the input end, the cellular-core opticalfiber comprising (i) a plurality of core regions, (ii) an inter-corecladding region surrounding and extending between the core regions, and(iii) an outer cladding surrounding the inter-core cladding region,wherein a refractive index of each of the core regions is larger than arefractive index of the inter-core cladding region; and directing aninput laser beam across the input end of the cellular-core optical fiberalong a path comprising one or more of the core regions, whereby atleast one of a beam shape or a beam parameter product of an output beamemitted at the output end of the cellular-core optical fiber isdetermined at least in part by the path of the input laser beam.
 2. Themethod of claim 1, further comprising modulating an output power of theinput laser beam as the input laser beam is directed along the path. 3.The method of claim 1, wherein the path comprises a portion of theinter-core cladding region.
 4. The method of claim 3, further comprisingreducing an output power of the input laser beam as the input laser beamis directed over the inter-core cladding region, thereby reducing orsubstantially eliminating coupling of beam energy into the inter-corecladding region.
 5. The method of claim 3, wherein beam energy coupledinto the inter-core cladding region contributes a non-zero backgroundenergy level to the output beam.
 6. The method of claim 1, wherein therefractive index of the inter-core cladding region is greater than arefractive index of the outer cladding.
 7. The method of claim 1,wherein the refractive index of the inter-core cladding region isapproximately equal to a refractive index of the outer cladding.
 8. Themethod of claim 1, wherein at least two of the core regions of thecellular-core optical fiber have different cross-sectional shapes in aplane perpendicular to a central axis of the cellular-core opticalfiber.
 9. The method of claim 1, wherein all of the core regions of thecellular-core optical fiber have the same cross-sectional shape.
 10. Themethod of claim 1, wherein the plurality of core regions of thecellular-core optical fiber comprises (i) a central core region and (ii)a plurality of outer core regions disposed around the central coreregion.
 11. The method of claim 10, wherein a diameter of the centralcore region is greater than a diameter of at least one of the outer coreregions.
 12. The method of claim 1, wherein none of the core regions isannular in cross-section.
 13. The method of claim 1, wherein the coreregions are not coaxial with respect to each other.
 14. The method ofclaim 1, wherein the path is selected based at least in part on a beamparameter sensed proximate the output end of the cellular-core opticalfiber.
 15. The method of claim 1, wherein the plurality of core regions,the inter-core cladding region, and the outer cladding all extend alongan entirety of a length of the cellular-core optical fiber.
 16. Themethod of claim 1, further comprising processing, with the output beam,a workpiece disposed proximate the output end of the cellular-coreoptical fiber.
 17. The method of claim 16, wherein the at least one ofthe beam parameter product or the beam shape of the output laser beam isdetermined, via selection of the path, based at least in part of acharacteristic of the workpiece.
 18. The method of claim 17, wherein thecharacteristic of the workpiece comprises at least one of a thickness ofthe workpiece or a composition of the workpiece.
 19. A method of forminga laser beam, the method comprising: providing a cellular-core opticalfiber having an input end and an output end opposite the input end, thecellular-core optical fiber comprising (i) a plurality of core regions,(ii) an inter-core cladding region surrounding and extending between thecore regions, and (iii) an outer cladding surrounding the inter-corecladding region, wherein a refractive index of each of the core regionsis larger than a refractive index of the inter-core cladding region; anddirecting an input laser beam into one or more of the core regions andinto the inter-core cladding region, whereby at least one of a beamshape or a beam parameter product of an output beam emitted at theoutput end of the cellular-core optical fiber is determined at least inpart by the one or more core regions into which the input laser beam isdirected.
 20. The method of claim 19, wherein, in a plane perpendicularto a central axis of the cellular-core optical fiber, at least two ofthe core regions of the cellular-core optical fiber have differentcross-sectional shapes and/or different cross-sectional sizes.
 21. Themethod of claim 19, further comprising processing, with the output beam,a workpiece disposed proximate the output end of the cellular-coreoptical fiber.
 22. The method of claim 21, wherein the at least one ofthe beam parameter product or the beam shape of the output laser beam isdetermined, via selection of the one or more core regions into which theinput laser beam is directed, based at least in part of a characteristicof the workpiece.
 23. The method of claim 22, wherein the characteristicof the workpiece comprises at least one of a thickness of the workpieceor a composition of the workpiece.
 24. A method of forming a laser beam,the method comprising: providing a cellular-core optical fiber having aninput end and an output end opposite the input end, the cellular-coreoptical fiber comprising (i) a plurality of core regions, (ii) aninter-core cladding region surrounding and extending between the coreregions, and (iii) an outer cladding surrounding the inter-core claddingregion, wherein a refractive index of each of the core regions is largerthan a refractive index of the inter-core cladding region; and directingan input laser beam into only one of the core regions while notdirecting any laser light into any of the other core regions, and,optionally, directing the input laser beam into the inter-core claddingregion, whereby at least one of a beam shape or a beam parameter productof an output beam emitted at the output end of the cellular-core opticalfiber is determined at least in part by the single core region intowhich the input laser beam is directed.
 25. The method of claim 24,wherein the input laser beam is directed into the one of the coreregions and into the inter-core cladding region.
 26. The method of claim24, further comprising processing, with the output beam, a workpiecedisposed proximate the output end of the cellular-core optical fiber.27. The method of claim 26, wherein the at least one of the beamparameter product or the beam shape of the output laser beam isdetermined, via selection of the single core region into which the inputlaser beam is directed, based at least in part of a characteristic ofthe workpiece.
 28. The method of claim 27, wherein the characteristic ofthe workpiece comprises at least one of a thickness of the workpiece ora composition of the workpiece.